1. Field of the Invention
The present invention relates generally to spooled tubing operations. More particularly, the present invention relates to a system for simultaneously translating and rotating spooled tubing within a wellbore. More particularly still, the present invention involves a system which permits simultaneous translation and rotation of spooled tubing to drill or conduct other downhole operations in a borehole extending into subterranean formations.
2. Description of the Prior Art
Standard rotary drilling rigs are typically comprised of a supportive rig floor, a derrick extending vertically above said rig floor, and a traveling block which can be raised and lowered within said derrick. During drilling operations, this rig equipment is often used to insert and, in many cases remove, tubular goods from a wellbore situated under the derrick which extends downward into subterranean formations. Frequently, drill bits and/or other equipment are lowered into such wellbores and manipulated within said wellbores via tubular drill pipe in order to conduct downhole operations within such wellbores.
During downhole well operations, pipe (such as, for example, drill pipe, tubing, workstrings and the like) is typically inserted in a number of sections of roughly equal length. These pipe sections, commonly referred to as “joints,” are typically installed one at a time, and screwed together or otherwise connected end-to-end to make a roughly continuous length of pipe. In order to start the process of inserting pipe in a well, a first joint of pipe is lowered into the wellbore at the rig floor, and suspended in place using a set of “lower slips.” The lower slips hold the weight of the pipe and suspend such pipe in place in the well.
Once a first joint of pipe is inserted into a well, said joint is generally positioned so that its top is situated a few feet above the rig floor. A rig crew or pipe handling machine can then grab a second joint of pipe, lift said second joint of pipe vertically into the derrick, position said second joint above the first joint (which was previously run into and hanging within the well), and “stab” a male or “pin-end” thread at the bottom of said second joint into a female or “box-end” thread at the top of the first joint. The second joint is then rotated in order to mate the threaded connections of the first and second joints together.
Thereafter, a set of elevators connected to the traveling block in the rig's derrick, which is attached to the second (upper) joint of pipe, can be raised to take weight off of the lower slips. The lower slips are then removed, allowing the entire weight of the pipe string to be suspended from the elevators attached to the rig's traveling block. Both the first and second joints of pipe can then be inserted into the well by lowering the traveling block. After the second or upper joint of pipe is lowered a sufficient distance into the well, the lower slips are again inserted in place near the rig floor. The aforementioned process is repeated until the desired length of pipe (i.e., the desired number of pipe joints) is inserted into the wellbore. The same process is typically utilized for many different types and sizes of pipe, whether small diameter workstring or large diameter drill pipe or casing.
In order to remove a string of pipe from a wellbore, the aforementioned process is essentially performed in reverse. That is, the pipe string can be removed from the wellbore using the rig's traveling block until a desired length of pipe is positioned above the rig floor. The lower slips are set, and the pipe is then unscrewed at a point above said lower slips. Thereafter, the loose section of pipe hanging from the traveling block is moved out of the vicinity of the wellbore; said pipe is typically “racked back” vertically within the derrick, or transferred to a horizontal pipe rack located apart from the derrick. This process is repeated until the desired length of pipe has been removed from a wellbore.
In recent years, oil and gas operators have discovered an alternative to conventional rig operations employing a continuous length of flexible tubing rather than multiple sections of rigid pipe. This alternative, commonly referred to as “coiled tubing”, utilizes a continuous length, up to 10,000 feet or more, of flexible tubing which is stored on a reel. Such conventional coiled tubing can be translated in and out of a wellbore in a virtually continuous manner without the need to continually connect and/or disconnect individual pipe sections as described above.
Conventional coiled tubing can be used to conduct numerous downhole operations. For example, coiled tubing can be concentrically inserted into an existing wellbore in order to clean out sand or other debris from such well. Further, conventional coiled tubing can be used to drill a borehole by attaching a hydraulic “mud motor” and drill bit to the distal end of the tubing, and then pumping pressurized drilling fluid through the coiled tubing. Such pressurized drilling fluid drives the hydraulic mud motor which, in turn, rotates the drill bit. The drill bit and hydraulic mud motor are lowered into the borehole as the coiled tubing is spooled off the reel, thereby drilling the borehole deeper into subterranean formations.
A significant advantage of coiled tubing operations over conventional rig operations is that the coiled tubing can be raised and lowered in a borehole at rates up to ten times faster than those possible with conventional rig techniques. This increased speed is primarily attributable to the fact that coiled tubing can be “tripped” in and out of a borehole without screwing or unscrewing individual joints of pipe during the process. In other words, the continuous coiled tubing can be translated in and out of a wellbore without having to stop to add or remove individual joints of pipe.
However, one significant disadvantage of conventional coiled tubing operations is the inability to rotate such tubing within a borehole. Because such conventional coiled tubing cannot be rotated relative to a borehole, during the drilling process all of the energy required to rotate a drill bit must be supplied by pressurized drilling mud which drives a downhole hydraulic mud motor. Further, when conducting downhole operations, it is frequently beneficial to rotate pipe in order to overcome friction between the inner surface of the borehole and the outer surface of the coiled tubing, particularly in highly deviated or horizontal wellbores. Such friction can frequently make it difficult to translate tubing in a borehole and/or to manipulate such pipe in a well. Further, the increased friction between the coiled tubing and the borehole may require more frequent tripping of such coiled tubing.
Attempts have been made to develop coiled tubing units which permit rotation of such tubing within a wellbore. However, such attempts involve complicated and cumbersome equipment which is not practical for most oil and gas operations, particularly where space is at a premium. Thus, it is advantageous to provide a compact, modular unit which allows for translation of pipe continuously into a wellbore while simultaneously permitting rotation of such pipe downhole.